This is a multicenter, pharmacokinetic study whereby HIV-infected subjects with culture-confirmed tuberculosis (TB), who are treated with any 2 or more of the following : rifampin, INH, ethambutol, or pyrazinamide, will have serum drug concentration determinations performed at two time points, in an effort to learn more about the absorbtion and the pharmacokinetics of these drugs in these subjects. Blood specimens will be collected at 2, 6, and 10 hours after the administration of the study medication, once between days 10-14 of a phase of daily treatment and once while on an intermittent dose regimen 3-times-per-week or 2-times-per-week within 8 weeks of completion of a daily dosing regimen.